[tropo]

Suppose it is just harmless to the computer, but it uses the USB port to power something else.

It could contain a microphone and a transmitter.

A more evil device, for assassination, could contain explosives or nerve gas. Plugging in the device is fatal.

[russdill]

Great plot device. When a certain file is opened, the nerve gas is released. Or when a file is saved with certain text or properties (author, etc).

However, I'm doubtful that a small USB drive would have enough volume to be effective. Wouldn't matter on TV though.